The United States officially opened its deeply controversial Jerusalem embassy on Monday in a ceremony that included a video address by President Donald Trump as deadly clashes broke out.

Trump told the ceremony that the United States remained committed to reaching a lasting Middle East peace, though the move of its embassy in Israel from Tel Aviv to Jerusalem has provoked outrage.

Read more: Pakistan expresses 'grave concern', joins others in condemning shifting of US embassy to Jerusalem

A plaque and seal were unveiled at the ceremony, officially opening the embassy.

Violent clashes had erupted along the Gaza Strip's border hours ahead of the controversial opening, leaving 52 Palestinians dead from Israeli fire and more than 2,400 wounded.

The dead included a 14-year-old, according to the Gazan health ministry.

Read: For Palestinians, US Embassy move a show of pro-Israel bias

It was the deadliest day in the Israeli-Palestinian conflict since a 2014 war between the Jewish state and Gaza's Islamist rulers Hamas.

Thousands had gathered near the border in protest while smaller numbers of stone-throwing Palestinians were approaching the fence and trying to break through, with Israeli snipers positioned on the other side.

Crowds had built throughout the day in the Palestinian enclave less than 100 kilometres away from Jerusalem and sealed off from Israel by a blockade.

The inauguration, which follows Trump's deeply controversial December 6 recognition of the disputed city as Israel's capital, also came at a time of heightened regional tensions.

It follows Trump's announcement last week that the United States is withdrawing from the Iran nuclear deal and Israeli strikes two days later on dozens of Iranian targets in Syria.

Those strikes came after rocket fire toward Israeli forces in the occupied Golan Heights that Israel blamed on Iran.

The Trump administration has vowed to restart the moribund Middle East peace process but the embassy move has inflamed tensions.

On Sunday, Al Qaeda leader Ayman al-Zawahiri released a message saying America's decision was evidence that “appeasement” has failed Palestinians and urged Muslims to carry out jihad against the US, according to a transcript provided by the SITE monitoring agency.

'Capital for all time'

Israeli Prime Minister Benjamin Netanyahu, who has repeatedly called Trump's decision “historic”, welcomed them at a reception on Sunday.

“Jerusalem has been the capital of the Jewish people for the past 3,000 years,” he said.

“It's been the capital of our state for the past 70 years. It will remain our capital for all time.”

Sullivan called the embassy “a long overdue recognition of reality”. Saeb Erekat, Palestine Liberation Organisation secretary-general, called it a “hostile act against international law”.

Around 1,000 police officers were being positioned around the embassy for the inauguration. Israel's army said it was almost doubling the number of troops surrounding Gaza and in the occupied West Bank.

It also dropped leaflets warning Gazans to stay away from the fence, including one with a photo of the Champs-Elysees boulevard in Paris and the caption: “Gaza 2025? The choice is in your hands.”

Israeli Defence Minister Avigdor Lieberman said in a message to Gazans “we will protect our civilians with all our means and not enable the fence to be crossed”.

Israelis began celebrating on Sunday, as tens of thousands marched in Jerusalem, some holding American flags, to mark Jerusalem Day.

The annual event is an Israeli celebration of the “reunification” of the city following the 1967 Six-Day War. Israel occupied the West Bank and east Jerusalem in 1967 and later annexed east Jerusalem in a move never recognised by the international community.

Beyond the disputed nature of Jerusalem, the date of the embassy move is also key. May 14 marks the 70th anniversary of the founding of Israel.

The following day, Palestinians mark the “Nakba”, or catastrophe, commemorating the more than 700,000 Palestinians who fled or were expelled from their homes in the 1948 war surrounding Israel's creation. Palestinian protests are planned on both days.

Trump calls embassy move 'a great day for Israel'

Trump hailed the scheduled opening of the US embassy in Jerusalem as “a great day for Israel”, even as deadly clashes erupted between Palestinians and Israeli security forces.

Trump made no reference to the violence in an early morning tweet, instead inviting Twitter followers to watch live coverage of the embassy opening on Fox News channels, which was to begin at 1300 GMT.

“Lead up to 9:00am (eastern) event has already begun. A great day for Israel!” Trump tweeted.

'Off the table'

There have already been weeks of protests and clashes along the Gaza border, with 70 Palestinians killed by Israeli fire there since March 30.

No Israelis have been wounded and the military has faced criticism over the use of live fire.

Israel says it only opens fire when necessary to stop infiltrations, attacks and damage to the border fence, while accusing Hamas, the movement that runs the blockaded Gaza Strip, of seeking to use the protests as cover to carry out violence.

Jerusalem's status is perhaps the thorniest issue in the Israeli-Palestinian conflict.

Israel considers the entire city its capital, while the Palestinians see east Jerusalem as the capital of their future state.

In the decades since 1967, international consensus has been that the city's status must be negotiated between the two sides, but Trump broke with that to global outrage.

He has argued that it helps make peace possible by taking Jerusalem “off the table”, but many have pointed out he has not announced any concessions in return from Israel.

Trump's initial decision led to a series of protests in various Middle Eastern and Muslim countries.